Onion Market Requirements

A uniform size, shape and color, plus freedom from soil and disease are important characteristics desired by the retailer and consumer. Bulbs should be sufficiently dry for the intended purpose. Firmness is also critical, particularly in dry bulb onions to be stored for long periods. Most common bulb onions have 10-12% dry matter. A thin neck size is also desirable as these onions are less susceptible to disease problems during the curing process.

Even size is important in onion production. Generally, large size bulbs get the best prices, provided shape and skin quality etc., are suitable. Taste, texture, smell and pungency vary between types and cultivars. Onions for fresh consumption without cooking are usually sweeter and mild flavored. They are generally larger – with just one center, thereby suitable for slicing into onion rings. Pungency is largely due to the level of sulfur based non-protein amino acids they contain.

Class I 

Bulbs that are: 

• Firm and compact 
• Unsprouted (free from externally visible shoots) 
• Free from swelling caused by abnormal development 
• Practically free of root tufts; 

Provided the keeping quality and presentation in the package is not affected they may have a slight defect in shape or color, a slight staining, superficial cracks in the skin, and an absence of part of the outer skins, provided the flesh is protected.

Class II 

Includes onions which do not qualify for Class I, but satisfy the minimum requirements specified above. They must be reasonably firm and can have some defects in shape, coloring, early signs of shoot growth visible from the outside, traces of rubbing, slight marking caused by parasites or disease. 

Within these two classes, an even size is important. Generally, large size bulbs fetch the best prices, provided shape and skin quality etc., are suitable. Onions for fresh consumption without cooking are usually sweeter and mild flavored. They are generally larger – with just one centre, thereby suitable for slicing into onion rings. 

When cut, damaged or eaten, sulfenic acids, ammonia and pyruvate are released giving a range of strong smells. Measurement of this important characteristic is difficult. While levels of pyruvate can be assessed, this does not always provide the complete answer to an onion’s ‘taste’ or pungency (Table 1). 

It is only when there is a low level of sulfur in the bulb that the sweetness is ‘allowed’ to come through in the taste. Thus, onion quality is usually assessed by taste panels that place onions, according to a combination of traits, into a range of ‘sensory rating’ categories. 

These vary according to country, but in the USA, onions are rated from 1 to 18. An onion rated 1 has very little pungency when raw. Any onion above 6 can’t be comfortably eaten raw, while most Vidalia and Super Sweet onions score 2.5-4.

Garlic 

Garlic needs to be free of rots, abnormal moisture, sprouts or any other damage. Cloves also need to be firm. The EU has defined three classes of garlic: 

Extra Class - Minimum diameter 45mm 
Intact bulbs, regular in shape and properly clean. Free of defects bar superficial blemishes. Cloves must be compact with roots cut off flush with the bulb. 

Class I - Minimum diameter 30mm 
Bulbs must be intact and of fairly regular shape. Slight tears in the outer skin are allowed and the cloves must be reasonably compact. 

Class II - Minimum diameter 30mm 
Garlic can have the following defects – tears in the skin or missing parts of the skin; healed injuries; slight bruises; irregular shapes and up to three cloves missing.

Leeks 

Leeks need to have a clean, long white pseudostem without a crooked stem or bulbous base. They are usually ridged up in the field to provide a long white base. Size and shape is important, with most retailers preferring leeks with a pseudostem diameter wider than 20mm and longer than 150mm and an average weight of around 160g. Uniformity of the bunch is important. Leeks are usually graded by size and are increasingly marketed trimmed and prepacked ready for cooking. 

Leeks are very hardy and can be left ridged up in the field during winter to be harvested when needed. They should not be allowed to bolt (go to seed).

Chives and Shallots 

Shallots are sold dried and loose in windowed trays or in small mesh bags. They should be free of rots. Bulb size is variable and depends on the variety. Some markets require bulbs that should be large enough to be peeled easily. Chives are sold fresh cut in bunches, as a whole plant, or chopped and frozen, dehydrated or freeze-dried, in small packs. Leaves should be green and fresh looking.

Japanese Bunching Onions 

These onions are normally sold as small green 40-90cm long shoots with tender leaves and long white blanched pseudostems.

Processed Products 

Processed products generally have a weaker flavor because of the breakdown of the sulfur containing compounds during processing. 

Concentrated oils are produced by steam distillation of garlic and onions. They are used to flavor processed foods. 

Onions grown for dehydration require higher dry matters of 17-20%. They are usually made from white-fleshed onions, but chives and leeks can also be processed in such a manner. 

Dried flakes can be ground to make powders, which are also used for flavoring in soups, sauces, etc. Small white-skinned varieties are more suited to pickling. They are usually peeled, fermented in brine and bottled in vinegar.